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neuro - yr 2 > structure and function of the eye > Flashcards

structure and function of the eye Flashcards

1
Q

what are the 3 types of tear production

A

basal tears

reflex tears - response to irritation - CN V1 afferent from cornea, efferent is PNS - NT is ACh

crying - emotional

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2
Q

describe the larcimal system *

A

biggest comp of teasrs produced by the lacrimal gland

drains through the 2 puncta, opening on the medial lid margin

flow through the superior and inferior canaliculi

gather in the tear sac

exit through tear duct into the nose

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3
Q

describe the tear film *

A

maintains smooth cornea-air surface, oxygen supply to cornea, rremoval of debris, bacteriocide

3 layers:

superficial oily layer to reduce tear film evaporation (produced by a row of meibomian glands along the lid margins)

aquous tear film - tear gland

mucinous layer on the corneal surface to maintain surface wetting from goblet cells - cushion and protect eye from infection.

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4
Q

what is teh conjunctiva *

A

thin transparant tissue that covers the outer surface of the eye

nourished by tiny bv nearly invisible to the naked eye

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5
Q

where is the cornea *

A

begins at the outer edge of the cornea, covers the visible part of the eye, lines the isnide of the eyelids

coats the sclera

fold in conjuctiva sack - protect structures around the eye

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6
Q

when do the blood vessels supplying the conjunctiva become visible *

A

conjuctavitis and conjunctival hyperaemia

uveitis - inflammation of the uvea

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7
Q

what is the vitreous *

A

structure in the eye that keeps it in its shape

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8
Q

what is the size of the eye *

A

24mm diameter

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9
Q

what are the 3 layers of the coat of the eye *

A

the sclera - hard and opaque

choroid - pigmented and vascular

retina - neurosensory tissue - transparant - light pass through and hit phototreceptors

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10
Q

describe the sclera *

A

commonly known as the white of the eye

tough opaque tissue that serves as the eye’s protective outer coat

high water content

coat for 2/3 of eye - then contuous with sclera

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11
Q

describe the cornea *

A

transparent

dome shaped window covering the front of the eye

powerful refracting surface, providing 2/3 of eyes focussing power - conves, higher refractive period than air

low water content

front most part of teh anterior segment

continious with the scleral layer

physical barrier

infection barrier

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12
Q

what is the structure of the cornea *

A

5 layers:

epithelium - external wall

Bowman’s mem - basement mem of epi

stroma - regularity contributes towards its transparancy, corneal nerve endings provide sensation and nutrients for healthy tissue, no bv in normal cornea

descemet’s mem - basement membrane for endotheliym

endothelium - pumps fluid out of cornea - preventing oedema - only 1 layer, no regeneration piowe , density decrease with age, dysfunction = oedema and cloudiness

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13
Q

what happens if you hydrate the cornea *

A

goes white

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14
Q

what is the uvea *

A

vascular coat of teh eye

between the sclera and the retina

composed of - iris, ciliary body and chroid

these 3 portions are closely connected - disease of 1 part affect the others

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15
Q

describe anterior intermediate and posterior uveitis *

A

anterior - normally transparant but in uveitis can see inflammatory cells - if dilate the pupil and look behind - it is still transparant - treat topically

intermediate and posterior - cells in the vitreous too - treat systemically

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16
Q

describe the choroid *

A

between the retina and sclera

coats the rretina

composed of layers of BV that nourish back of eye

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17
Q

describe teh blood supply of the retina *

A

2 blood supplies

from choroid - supply outer part of the retina

inner retinal arteries from the central retinal vein that gives off the central retinal artery - noruishh the inside of retina

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18
Q

what is teh retina *

A

very thin layer of tissue

lines the inner part of the eye

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19
Q

function of the retina *

A

capture the light rays that enter the eye

impulses are sent to the brain for processing via the optic nerve

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20
Q

describe the optic nerve *

A

transmit electrical impulses from the retina to the brain

connects to back of eye near macula

visible portion is called the optic disk

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21
Q

describe how you can see the nerves in the eye

A

using polarised/red light

optical coherence tomography - see thickness of the nerves

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22
Q

what is the importance of looking at the bv at the back of the eye

A

abnormalities here reflect abnormalities in the rest of the bv

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23
Q

what is the macula *

A

small, highly sensitive part of retina - responisible for detailed central vision

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24
Q

describe the anatomy of the fovea *

A

located roughly in centre of the retina

avascular

fovea at teh centre

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25
Q

role of the macula *

A

appreciate detail

perform tasks that require central vision eg reading

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26
Q

what is the 1st cause of irrevesible blindness *

A

glaucoma - silent until late stages

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27
Q

what are the landmarks in the eye *

A

the optic disk

the macula - avascular

bv - clsoer to optic disk = thicker

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28
Q

what are the anterior and posterior segments of the eye *

A

anterior segment - ocular structure, anterior to the lense

posterior - ocular structure posterior to the lens

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29
Q

describe the anterior chamber *

A

between the cornea and the lense

filled with clear aq fluid

supplies nutrients

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30
Q

describe the posterior chamber *

A

between the posterior aspect of the iris and the zonula

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31
Q

role of ciliary body *

A

production of aq humour

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32
Q

path of the aq humour *

A

produced by the ciliary epi

pass through post chamber

through pupil

fill the anterior chamber

drain into angle by the trabecular meshwork - schlemm’s canal - specialised vein draining 80% fluid, rest is drianed passively by uveal scleral outflow

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33
Q

function of the aq humour *

A

supplies glucose to cornea

34
Q

normal intraocular pressure *

A

12-24mmHg

35
Q

definition of glaucoma *

A

optic neuropathy with characteristic structural damage to the optic nerve

associated with progressive retinal ganglion cell death, loss of nerve fibres and visual field loss

36
Q

describe glaucoma *

A

risk factor is raised intraocular pressure - not essential, can have raised pressure and not glaucoma and vice verca

age, family history and ethnicity also risk factors

have retinal ganglion cell death and enlarged optic disk cupping

cause visual field loss and blindness

37
Q

treatment of raised intraocular pressure *

A

medical

surgery - increase outflow or reduce production

parasurgery - lasers - create drainage hole on iris

38
Q

wat are the 2 types of glaucoma, describe them *

A

primary open angle glaucoma - commonest - trabecular meshwork dysfunction

closed angle gaucoma - acute/chronic - increased pressure pushes the iris/lens complex forward - block the trabecular meshwork - risk factors: small eye, narrow angle at trabecular meshwork - may present with sudden painful redeye and acute drop in vision

39
Q

wat would you see with glaucoma *

A

missing details - brain fills in areas tjat you cant see with things that are around it

40
Q

what is the visual difference between arterioles and venules in the eye

A

venules - thicker and darker

41
Q

why is the optic nerve a blind spot *

A

no photoreceptors here - dont normally notice it becausse the brain fills in the gap

if sudden change here - brain cant fill gap - see black

42
Q

describe photoreception in the fovea *

A

highest concentration of cones - able to percieve detail

low conc of rods - which are more sensitive to light than cones- why objects in periphery look brighter

43
Q

descrive central vision *

A

detail and colour vision

reading and facial recognition

assessed by the visual acuity assessment

(from fovea)

44
Q

describe peripheral vision *

A

shape movement and night vision

navigation

assessed by visual field assessment

loss = unable to navigate in environment - may need white stick even witth perfect central vision (vision acuity)

45
Q

describe the retinal structure *

A

outer layer (1st order neuron) - detection of liught

middle layer (2nd order) - bipolar cells - local signal processing to improve contrast sensitivity and redulate sensitivity

inner layer (3rd order) - retinal ganglion cells - transmission of ssignal from eye to brain

46
Q

describe the orientation of photoreceptors in the retina *

A

face away from the pupil

light bounce on retinal pigment epi then hit the photoreceptors - some hit teh straight aprt and some hit the curved part (rretina is curved) - poroprtion of retina that is hit tells us position is space

pupil black because light isnt reflected back out becuase rretina epi is dark so absorbs most of light - only see ‘red reflex’ when shine light directly into eye

47
Q

describe rods *

A

they have a longer outersegment with phhottosensitive pigment

100x more sensitive to light than cones are

slow response to light

scotopic vision (night)

120 million rods

48
Q

describe cones *

A

less sensitive to light

faster response than rods

photopic visiion (day and colour)

6 million

49
Q

describe the photoreceptor distribution relative to fovea *

A

no receptors in the blind spot - 10-20 degrees

cones peak at 0 degrees

rods peak at 20-40 degrees

50
Q

describ ethe frequency spectrum *

A

S cones - blue light 400-450 nm (WL)

M cones - green - 530-560

L cones - red - 560-600

rods - 500nm

UV - less than 400nm

blue laser - see front of retina, greenn- intermediate, red- deep

51
Q

what is the most common colour deficiency *

A

deuteranomaly - confusion of red and green

also called daltonism

52
Q

what is acromatopsia *

A

total colour blindness - just see grey etc

53
Q

what is the ishihara test *

A

colour perception test

ishihara plates test for red-green deficincies only

plates with circles occuring randomly in size

normal will see teh correct 2 diugit number

abnormal - no number/wrong

54
Q

what is special about number 25 of the ishihara test *

A

everyone can see - even with acromatopsia - look different shhades of grey

55
Q

what is dark adaption *

A

increase in light sensitivity in dark

photoreceptors are firing all the time - so when see bright light, they continue firing afterwards - so keep seeing the bright image - so need to dark adapt for a length of time

biphasic process - cone adaption for 7minutes, rod adaption for 30minutes

56
Q

describe light adaption *

A

adaption from dark to L occurs over 5 mins

bleaching of photopigments

neuroadaption

inhibition of cone rod function

57
Q

wat is refraction *

A

as light goes from 1 medium to another, the velocity changes

as light goes from 1 medium to another, its path changes

58
Q

what is an index of refraction

A

= speed light in vacuum/speed light in medium

always >/=1

59
Q

what does light do when it hits a new medium *

A

some light reflects off teh boundayr

some refracts

angle of incidence = angle of reflection

60
Q

what does a converging lense do *

A

takes light rays and brings them to a point

61
Q

what does a concave lense do *

A

takes ligt rays and spread them out

virtual focal point behind the lense

62
Q

what is emmetropia *

A

there is adequate correlation between axial length and refractive power - parallel light rays fall on the retina - no accomodation

63
Q

what is ametropia *

A

mismatc between axial length and retractive power

parallel light rays dont fall on the retina

eg

nearsightedness - myopia

farsightedness - hyperopia

astigmatism

presbyopia

64
Q

what is myopia *

A

parallel rays converge at a point anterior to the retina

eitiology not clear - genetic factor

causes - excessive long globe (axial myopia) more common

excessive refractive powerr (refractive myopia) - cornea/lense are too convex

from clsoe objects light rays come from an angle - so focal point is further away = can read

65
Q

symptoms of myopia *

A

blurred distance vision

squint too improve visual acuity when gazing into distance - trying to only get light ocming straight so that it doesnt get refracted

66
Q

treatments for myopia *

A

concave lense - make rays diiverge = focal point on retina

contact lens

refractive surgery - flattern the cornea = reduced refraction

remove lens and hence refrcctive power - not done anymore

67
Q

what is hyperopia *

A

parallel rays converge at a focal point posterior to the retina

eitiology not clear - inherited

causes: excessive short globe (axial hyperopia) - common, insufficient refractive power (refractive hyperpia) - lens flatter, can accomodate within acertain degree

68
Q

symptoms of hyperopia *

A

visual acuity tends to blur early - either cant read fine print, or is fine and then suddemnly and intermittently blurry - worse when lighting weak, tired, print is weak

asthenopic problems - eyepain, headache in frontal region, blurring sensation in eye, blepharoconjunctavitis

amblyopia - uncorrected hyperopia - ?

69
Q

treatment for hyperopia *

A

convex glasses

contact lensess

intraoptic therapy

70
Q

what is astgmatism *

A

parallel rays come to focus in 2 focal lines rater than 1

eitiology - herefditory

casue - cornea not spherical - refract differently along one meridian compared to a perpendicular meridian = >2 focal points

punctifom object present as 2 sharply defined lines

2nd focal point wont fall on the retina - confusing the images taht you see `

71
Q

symptoms of astigmatism *

A

asthenic problems - headache, eye pain

blurred vision

distortion of vision

head tiliting and turning

confusion of images

72
Q

treatment of astigmatism *

A

regular atigmatism - cyliinder lenses with or without spherical lenses (convex/concave) - light passing throug centre will not be refracted, light passing through edge hit concave - bend - reach focal point - roate it to correct just 1 area

irregular astigmatism - rigid contact lenses, surgery

73
Q

what is the near response triad *

A

for adaption to near vision

  • pupillary miosis (sphincter pupillae constrict) to increase the depth of field
  • convergence (medial recti from both eyes) - to align both eyes to a near object
  • accomodation (circular ciliary muscle) increase refractive power of lens for neaar vision
74
Q

what is presbyopia *

A

naturally occuring loss of accomodation - focus on near

onset from 40yrs

distant vision in tact

corrected by reading glasses (convex lenses) to increase the refractive power of the eye

75
Q

treatment for presbyopia *

A

convex lenses for near vision - reading glasses, bifocal, trifocal, progrressive power glasses

76
Q

what are the different types of optical correction *

A

specticals - monofocals (spherical lenses, cylindrical) multifocal

contacts - higher quality of optical image and less affect on the size of the retinal image than specticals, indication - aesthetic, athletic, occupational, irregular corneal astigmatism, high anisometropia, corneal disease

77
Q

disadvantages and complications of contact lenses *

A

careful daily cleaning, disinfection, expense

infectious keratitis, giant papillary conjunctavitis, corneal vascularisation, severe chronic conjuctavitis

78
Q

describe intraocular lenses *

A

replacement of cataract crystaline lense

give best correction for aphakia, avoid significant magnification and distortion by specticals

79
Q

describe surgical correction *

A

keratorrefractive surgery - RK, AK< PRK, LASIK, ICR, thermokeratoplasty

intraocular surgery - clear lens extraction, phakic intraocular lens implantation - but lens in front of the natural lens

laser surgery - remove he epithelium of the cornea, make a flap, use laers to adjust the cornea, return flap

phacoemulsification - remove the natural lens and implant of artifial folded lens

80
Q

describe the macula and fovea *

A

macula lutea is the pigmented region at the centre of the retina - 6mm diameter

fovea - pit at centre - no overlapping ganglion cell layer- highest conc of photoreceptors for fine vision

81
Q

how can you clinically asssess the eye

A

opyical coherence tomography - send diff wl into eye - pick up differnet structures - can reconstruct the eye

see fluid, attachments and path

82
Q

describe the process of accomodation *

A

contraction of the circular ciliary muscle inside the ciliary body

= relaxed zonules betweenciliary body attachment and lens capsule attachment

lens returns to natural convex shape due to elasticity- increasing the refractive power of the lens

this is mediated by CN 3

neuro - yr 2 (24 decks)

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